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Page:Popular Science Monthly Volume 21.djvu/265

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HYDRODYNAMICS AND ELECTRICITY.

pole. If, now, having one of the drums mounted in the water, and the other held in the hand, we bring them near each other while both are dilating or both are contracting that is, while both are in the same phase of pulsation—attraction will take place between them. The mounted drum will assume the direction of approach toward the one held in the hand, and of following it when it is removed; but if they are in opposite phases—if one is swelling while the other is contracting—they will be repelled. Like poles attract, unlike ones repel. The phenomena are the inverse of what are observed in ordinary electricity and magnetism, where unlike poles attract and like ones repel. The pulsating drum in these experiments represents an isolated pole, a conception which physicists have not hitherto regarded as possible.

Spheres of invariable volume, but adjusted so as to oscillate in either an horizontal or vertical direction, maybe used instead of the pulsating drums, when the phenomena assume a modified shape. The oscillators used by Professor Bjerknes are mounted as in the figure (Fig. 1, 3), where the sphere on the left is arranged so as to oscillate horizontally, and the one on the right to oscillate vertically, the alternate movements of oscillation being produced, like the pulsations of the drums, by alternately forcing in and withdrawing the air. The opposite sides of the sphere assume opposite phases, and the sphere acts like a magnet. If a sphere is brought near a pulsator, so that its oscillating movement shall be toward the drum while that is dilating, attraction takes place; but, if it be turned in the opposite direction, so as to be moving away from the drum while the same is swelling, repulsion will be manifested.

If two oscillating spheres be brought near each other, attraction takes place in case they are both moving to or from each other; repulsion, in case they are both moving in the same direction: and the change can be effected at once, as before, by turning one of the spheres around.

Professor Bjerknes has a considerable variety of apparatus for modifying the aspects of the phenomena by changing the relative situations of the bodies to each other, in all of which manifestations of an inverse character to those of ordinary magnetism are developed. If one of the spheres be mounted so as to be free to move about a vertical axis, it is found that, when a second oscillating sphere is brought near to it, the one that is free turns round its axis, and sets itself so that both spheres shall be simultaneously approaching or receding from each other. Two oscillating spheres mounted at the extremities of an arm, with freedom to move, behave with respect to another oscillating sphere exactly like a magnet; in the neighborhood of another magnetic pole. These directive effects are believed by Professor George Forbes to be perfectly new, both theoretically and experimentally.

The phenomena of attraction and repulsion, described above, are